Wells are frequently completed with a “horizontal tree”, i.e., a production system which contains one or more hangers in a spool body with a lateral production passageway in fluid communication with a production tubing string, and a tree cap above the tree hanger. A port through the spool body passes production fluids from the production tubing laterally through the spool body and then to the surface via a production flow line. Retrievable plugs are commonly installed in the bores of both the tree cap and the tubing hanger. Exemplary prior art is disclosed in U.S. Pat. Nos. 5,544,707, 5,706,893, 6,050,339, 6,039,119, 6,227,300, and 6,470,968. Relevant publications are U.S. 2001/0011593, 2002/000322 2002/0000315, 2003/0089501 and WO01/73259.
Various types of equipment and techniques have been proposed for the workover of horizontal spool tree wells. Workover operations are conventionally performed utilizing a floating drilling rig with a subsea BOP connected to the top of the horizontal spool tree, and a drilling riser connected to the top of the BOP. When a big bore riser and a BOP stack are placed on top of the tree, various types of workover operations may be performed, including pulling and reinstalling the tubing. One or more workover strings provide fluid communication with the horizontal spool tree assembly, with the workover fluid passing through the tree cap and to the tubing annulus. A running tool may be used to seal off the top of the tubing hanger and to pull a plug if one is provided in the top of the tubing hanger to close off the tubing string.
Workover porting of the tubing annulus may be accomplished utilizing valves in a line extending through the tubing hanger for fluid communication with the tubing annulus. Valves external of the spool body or within the spool body have alternatively been used to route the tubing annulus line around the tubing hanger to various locations within the spool body.
Horizontal spool trees also desirably provide a crossover line between the production line and the annulus line. If for some reason the production line needs to be shut down, flow may be diverted through the crossover line to the annulus line and then to the production platform. The crossover flow line is thus located closely adjacent the horizontal spool tree assembly, and conventionally is located within twelve feet of the production bore.
Horizontal spool trees also include an annulus port and an annulus line which conventionally extends from the spool tree assembly to the production platform. The annulus line enables annulus pressure which is excessive to be bled off, thereby maintaining a desired pressure differential between the interior and the exterior of the tubing string.
The disadvantages of the prior art are overcome by the present invention, and a horizontal spool tree with improved porting is hereafter disclosed.